MELBOURNE: Tens of thousands of Melbourne homes and businesses lost power Friday as air-conditioners taxed the power supply on what was forecast to be the hottest day in a decade for Australia's second-largest city.

The Victoria state capital, with a population of 5 million, is set to reach 44C. That would be Melbourne's hottest day since Feb 7, 2009 — a day of catastrophic wildfires that is remembered as Black Saturday.

That day, the temperature soared to 46.4C. Wildfires killed 173 people and razed more than 2,000 homes in Victoria.

Scores of wildfires are raging in heatwave conditions across much of drought-parched southeast Australia, with authorities warning the fire risk is high.

Audrey Zibelman, chief executive of the Australian Energy Market Operator, which manages the national electricity grid, said three generators had failed in Victoria and a fourth was expected to shut down on Friday.

As temperatures climbed in the early afternoon, 30,000 households and businesses at a time were switched off for as long as two hours so that supply could keep up with demand, Ms Zibelman said. Essential services such as hospitals were supplied with power.

Black Saturday had been the hottest day ever recorded by a major Australian city until Adelaide reached  46.6C on Thursday.

The South Australia state capital of 1.3 million people — 640km west of Melbourne — beat its previous 80-year-old record of 46.1C set on Jan 12, 1939, and records tumbled in smaller towns across the state.

The South Australian town of Port Augusta, population 15,000, topped the state at 49.5C.

The Australian Open tennis tournament in Melbourne invoked its extreme-heat policy on Thursday and closed the main stadium's roof during a women's semi-final match.

Last year was Australia's third-warmest on record.